Some Consistency Conditions for Dynamic Traffic Assignment Problems

This paper explores some critical issues in modeling network traffic flow for predictive user optimal dynamic traffic assignment. They include the role of FIFO (first-in-first-out) in link, path and network traffic dynamics, minimal set representation of link traffic evolution, and consistency conditions for link models. It is found that (1) link FIFO plays a central role in modeling link, path and network traffic flow evolution, and (2) the dimension of a minimal state set that adequately describes link traffic flow under FIFO is two. Moreover, two sufficient FIFO conditions are provided, and pitfalls in using these conditions to enforce FIFO are pointed out. Finally, ramifications of these findings to DTA modeling are also discussed.     

A Comparative Study of Some Macroscopic Link Models Used in Dynamic Traffic Assignment

As network loading forms the basis of many dynamic traffic assignment solution algorithms, we consider in this paper four macroscopic link models that are widely used in DTA studies as the building blocks of certain network loading procedures. For the same generic link, the four models are solved and evaluated numerically for various link inflow profiles under a single-destination framework. And the characteristics of each model is analyzed and compared with others from multiple perspectives such as algorithmic implementation, model calibration, model accuracy, computational time and memory consumption. It is our purpose to find the best link model for the development of realistic and efficient network loading procedures. Moreover, since model discretization and calibration substantially influence a link models performance, both issues are carefully addressed in the paper.     

Analytical Models of the Dynamic Traffic Assignment Problem

A review of analytical formulations of the dynamic traffic assignment problem is presented, focusing on the authors' experience with variational inequality approaches. Solution algorithms and computational issues requiring additional study are discussed.     

A Decomposition Scheme for System Optimal Dynamic Traffic Assignment Models

In this paper, a Dantzig-Wolfe decomposition based solution algorithm is developed for the linear programming formulation introduced by Ziliaskopoulos (2000) for System Optimal Dynamic Traffic Assignment problem. The algorithm takes advantage of the network structure in the constraint set of the formulation: the sub-problem is formulated as a minimum-cost-flow problem and the master as a simpler linear programming problem, which allows DTA to be solved more efficiently on meaningful networks. The algorithm is tested on an example network and its performance is analyzed.     

Continuous and Discrete Trajectory Models for Dynamic Traffic Assignment

A continuous trajectory model is presented in which transportation networks are represented as topological constructs. The general formulation enhances existing analytic dynamic traffic assignment models by incorporating continuous single-link traffic flow models in a general, coherent, and relatively intuitive manner. Specific exact formulation based on a simplified kinematic wave traffic flow model with physical queues is presented as well.A discrete trajectory model is proposed as an approximation of the continuous model. The discrete model provides wide flexibility in choosing the level of aggregation with respect to time intervals, ranging from several hours, as typical in current practice of long-term travel forecasting models, to one second or less, as in microscopic simulations. An algorithm to find discrete approximate solutions is presented as well as accuracy measures to evaluate them. The effect of time resolution on model performance is examined by a numerical example.     

Foundations of Dynamic Traffic Assignment: The Past,the Present and the Future

Dynamic Traffic Assignment (DTA) has evolved substantially since the pioneering work of Merchant and Nemhauser. Numerous formulations and solutions approaches have been introduced ranging from mathematical programming, to variational inequality, optimal control, and simulation-based. The aim of this special issue is to document the main existing DTA approaches for future reference. This opening paper will summarize the current understanding of DTA, review the existing literature, make the connection to the approaches presented in this special issue, and attempt to hypothesize about the future.     

面向动态交通分配的路段费用函数建模研究

在交通分配的研究中,车辆在路段上的行驶费用是决定网络交通流分布的关键因素之一。论文面对动态交通分配建模需要,在网络饱和条件下,对车辆在路段上的行驶时间进行了分析和建模。详细讨论了饱和交通网络中考虑容量约束下的车辆连续行驶时间和路口延误时间,在排队延迟模型中考虑了车辆的实际长度及由此而带来的影响,建立了离散的函数模型。最后给出计算实例,对比了点排队和实际排队的不同。     

The CONTRAM Dynamic Traffic Assignment Model

CONTRAM is a computer model of time-varying traffic in road networks, which takes as input the network definition and time-varying demand for travel between a set of origin and destination zones, and outputs the resulting network flows, routes and travel times. It combines a macroscopic time-sliced traffic model with disaggregate dynamic assignment of traffic, so is intermediate between macroscopic equilibrium and microscopic models. The paper details the methods used, including time-dependent queuing which plays a central role, and the treatment of network definition, user classes, road capacities, signals and coordination, vehicle emissions, Intelligent Transport Systems and research lines.     

改进粒子群算法在动态交通分配问题中的应用

在分析常规粒子群优化算法的基础上,针对动态交通分配问题,采用一种带变异因子的改进的粒子群优化算法,并根据粒子群的群体适应度标准差和理论最优值,给出收敛判断的依据。实验表明该算法具有简单、高效、快速的特点。     

交叉口有交通信号控制时用户最优动态配流模型

针对智能交通系统（ＴＴＳ）基础上中主要基础理论之一的动态交通分配问题,在现有研究成果的基础上,提出了更接近真实路网的多起点多旋点交叉口设置有交通信号控制（Ｔｒａｆｆｉｃ Ｓｉｇｎａｌ Ｃｏｎｔｒｏｌ）时的动态配流模型,给出了对现有的通过Ｆｒａｎｋ Ｗｏｉｆｅ算法所得的ＤＵＯ配流解进行修正的原则,最后的算例表明由修正后的模型和算法所得到的ＤＵＯ配流解满足ＴＳＣ约束。     

Research on Combined Dynamic Traffic Assignment and Signal Control

This paper presents a generalized bi-level programming model of combined dynamic traffic assignment and traffic signal control,and especially analyzes a procedure for determining the equilibrium queuing delays on saturated links for dynamic network signal control satisfying the FIFO (first-in-first-out)rule.The chaotic optimal algorithm proposed in this paper can not only present the optimal signal settings,but also calculate,at each interval,the link inflow rates and outflow rates for the dynamic user optimal problem,and provide real-time information for the travelers.Finally,a numerical example is given to illustrate the application of the proposed model and solution algorithm, and comparison shows that this model has better system performance.     

动态交通分配与信号控制的组合模型及算法研究

This paper presents a generalized bi-level programming model of combined dynamic traffic assignment and traffic signal control, and especially analyzes a procedure for determining the equilibrium queuing delays on saturated links for dynamic network signal control satisfying the FIFO (first-in-first-out) rule. The chaotic optimal algorithm proposed in this paper can not only present the optimal signal settings, but also calculate, at each interval, the link inflow rates and outflow rates for the dynamic user optimal problem, and provide real-time information for the travelers. Finally, a numerical example is given to illustrate the application of the proposed model and solution algorithm, and comparison shows that this model has better system performance.     

Stochastic Equilibrium Traffic Assignment with Value-of-time Distributed Among Users

In this paper, existing fixed-point models for stochastic equilibrium traffic assignment to transportation networks are extended to deal with the value of time distributed among users. This problem is relevant when transporation demand management measures affecting travelling monetary costs are to be evaluated. Analysis of existence and uniqueness of solutions is carried out, leading to mild assumptions about link cost-flow functions, path choice model, and value-of-time distribution. Some quite simple solution algorithms are also specified and their convergence analysed. Results of some applications are also reported.     

基于改进遗传算法的动态交通分配优化研究

传统的优化算法大多数由于计算量大或者容易使性能指标落入局部最优值而严重制约了模型的应用与发展,而用遗传算法等新的智能算法求解则会很简洁和方便。文章针对遗传算法在应用中存在的局限性,采用了小生境技术的遗传算法,结合精英保留策略、种群多样性保持方案、新的适应度值标定方式等改进遗传算法。通过对动态交通分配的特点分析,建立了动态交通分配模型,利用改进的遗传算法对模型进行求解。仿真结果体现了动态交通分配模型的有效性和改进遗传算法的优越性,大大提高了动态交通分配模型的实用价值。     

最优动态配流问题的离散模型及其解

对一般路网建立了具有良好结构形式的离散动态配流模型，该模型在多起点单讫点路网中的最优解满足交通流守恒约束和动态平衡原则。在提出了完全不同路段概念的基础上，对最优解的奇异性进行了分析，得到稳态最优解为非奇异解的结论。给出的算例验证了结论的正确性。     

动态平衡运量配流问题及其稳态伴随解算法

动态平衡运量配流问题的建模和求解是发展智能车辆导驶系统的理论基础.本文对多起点单讫点交通网络建立了连续时间最优控制模型,该模型的最优解对应于动态用户平衡解.文中提出的稳态伴随解算法避免了解复杂的两点边界值问题,可以获得原问题的近似解.该算法利用了交通网络和计算机网络的结构特性,计算速度较高,可用于城市交通流的实时控制.     

Stochastic User Equilibrium Traffic Assignment with Turn-delays in Intersections

Turn-delays in intersections contribute significantly to travel times and thus route choices in urban networks. However, turns are difficult to handle in traffic assignment models due to the asymmetric Jacobian in the cost functions. The paper describes a model where turn delays have been included in the solution algorithm of Stochastic User Equilibrium (SUE) traffic assignment. When the Jacobian is symmetric, SUE minimises the road users' 'perceived travel resistances'. This is a probit-model where the links cost-functions of the links are traffic dependent. Hereby, overlapping routes are handled in a consistent way. However, no theoretical proof of convergence has been given if the Jacobian is asymmetric, although convergence can be shown probable for model data representing realistic road-networks. However, according to the authors knowledge SUE with intersection delays have not been tested earlier on a full-scale network. Therefore, an essential part of the paper presents practical tests of convergence. Both geometric delays and delays caused by other turns are considered for each turn. Signalised and non-signalised intersections are handled in different ways, as are roundabouts. In signalised intersections a separate model handles queues longer than one green-period. Green-waves can also be taken into consideration. The model has been tested on a large-scale network for Copenhagen with good results. To make it possible to establish the comprehensive data, a GIS-based 'expert system' was implemented (see Nielsen, O.A., Frederiksen, R. D. and Simonsen, N. (1997). Using expert system rules to establish data on intersections and turns in road networks. International Transactions in Operational Research , 5 , 513–529.     

A Hybrid Deployable Dynamic Traffic Assignment Framework for Robust Online Route Guidance

Randomness in time-dependent origin-destination (O-D) demands and/or network supply conditions, and the computational tractability of potential solution methodologies are two major concerns for the online deployment of dynamic traffic assignment (DTA) under real-time traffic management systems. Most existing DTA models ignore these concerns and/or make unrealistic assumptions, precluding their online applicability. In this paper, a hybrid approach consisting of offline and online strategies is proposed to address the online stochastic dynamic traffic assignment problem. The basic idea is to address the computationally intensive components offline, while efficiently and effectively reacting to the unfolding conditions online. The offline component seeks a robust initial solution vis-à-vis randomness in O-D demands using historical O-D demand data. Termed the offline a priori solution, it is updated dynamically online based on unfolding O-D demands and incidents. The framework circumvents the need for accurate O-D demand and incident likelihood prediction models online, while exploiting historical O-D demand and incident data offline. Results of simulation experiments highlight the robustness of the hybrid approach with respect to online variations in O-D demand, its ability to address incident situations effectively, and its online efficiency.